Generally, applications with 5 v electric source voltage domain must be guaranteed to function properly with an electric source at 5.5 v, due to requirement of + or −10% for the operational voltage. On the other hand, while a minimum deviation of a VD (voltage detector which determines whether the voltage surpasses the high voltage alarming threshold by detecting the voltage) for high voltage alarming is required not to interfere with normal operation at 5.5 v, a high voltage alarming voltage might exceed 6 v. For example, a typical high voltage alarming VD at 6v+/−0.4 v has a minimum voltage 5.6 v which is greater than the normal operational voltage 5.5 v, and a maximum voltage 6.4 v, implicating that a high voltage alarm might be set off at 5.6 v, or 6.4 v, or any other value in the range of 6v+/−0.4 v. As 5v CMOS is concerned, the device can still function for a source voltage of 6.4 v, resulting in substantial substrate current leakage which will seriously impact the accuracy of the band-gap reference source.